hi guys i just picked up a1986 200sx for my kid i got it home and every thing looks good except it backfires alot when you let off the throttle,every thing is stock on the bike except an uni air filter ,i changed the spark plug and drained & refilled gas w/new. any suggestions?

 

open up the fuel air mixture screw

 

i tried that and it wants to stall do know how many turns it should be set at?

 

hey i also hear kind of a knocking every 15 to 30 seconds at idle from the crank case any ideas?